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Diffstat (limited to 'Documentation/arm64')
| -rw-r--r-- | Documentation/arm64/memory.txt | 73 |
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diff --git a/Documentation/arm64/memory.txt b/Documentation/arm64/memory.txt new file mode 100644 index 000000000000..dbbdcbba75a3 --- /dev/null +++ b/Documentation/arm64/memory.txt @@ -0,0 +1,73 @@ + Memory Layout on AArch64 Linux + ============================== + +Author: Catalin Marinas <catalin.marinas@arm.com> +Date : 20 February 2012 + +This document describes the virtual memory layout used by the AArch64 +Linux kernel. The architecture allows up to 4 levels of translation +tables with a 4KB page size and up to 3 levels with a 64KB page size. + +AArch64 Linux uses 3 levels of translation tables with the 4KB page +configuration, allowing 39-bit (512GB) virtual addresses for both user +and kernel. With 64KB pages, only 2 levels of translation tables are +used but the memory layout is the same. + +User addresses have bits 63:39 set to 0 while the kernel addresses have +the same bits set to 1. TTBRx selection is given by bit 63 of the +virtual address. The swapper_pg_dir contains only kernel (global) +mappings while the user pgd contains only user (non-global) mappings. +The swapper_pgd_dir address is written to TTBR1 and never written to +TTBR0. + + +AArch64 Linux memory layout: + +Start End Size Use +----------------------------------------------------------------------- +0000000000000000 0000007fffffffff 512GB user + +ffffff8000000000 ffffffbbfffcffff ~240GB vmalloc + +ffffffbbfffd0000 ffffffbcfffdffff 64KB [guard page] + +ffffffbbfffe0000 ffffffbcfffeffff 64KB PCI I/O space + +ffffffbbffff0000 ffffffbcffffffff 64KB [guard page] + +ffffffbc00000000 ffffffbdffffffff 8GB vmemmap + +ffffffbe00000000 ffffffbffbffffff ~8GB [guard, future vmmemap] + +ffffffbffc000000 ffffffbfffffffff 64MB modules + +ffffffc000000000 ffffffffffffffff 256GB memory + + +Translation table lookup with 4KB pages: + ++--------+--------+--------+--------+--------+--------+--------+--------+ +|63 56|55 48|47 40|39 32|31 24|23 16|15 8|7 0| ++--------+--------+--------+--------+--------+--------+--------+--------+ + | | | | | | + | | | | | v + | | | | | [11:0] in-page offset + | | | | +-> [20:12] L3 index + | | | +-----------> [29:21] L2 index + | | +---------------------> [38:30] L1 index + | +-------------------------------> [47:39] L0 index (not used) + +-------------------------------------------------> [63] TTBR0/1 + + +Translation table lookup with 64KB pages: + ++--------+--------+--------+--------+--------+--------+--------+--------+ +|63 56|55 48|47 40|39 32|31 24|23 16|15 8|7 0| ++--------+--------+--------+--------+--------+--------+--------+--------+ + | | | | | + | | | | v + | | | | [15:0] in-page offset + | | | +----------> [28:16] L3 index + | | +--------------------------> [41:29] L2 index (only 38:29 used) + | +-------------------------------> [47:42] L1 index (not used) + +-------------------------------------------------> [63] TTBR0/1 |